| 摘要 |
<P>PROBLEM TO BE SOLVED: To perform tone squelch determination at a low calculation cost and at a high speed. <P>SOLUTION: A tone signal circuit, after extracting a tone signal component from the demodulation signal of a receiver using analogue LPF, determines presence of the tone signal component at a wanted frequency by digital signal processing, with the digital demodulation signal that has been A/D converted (S1) as an input. The digital demodulation signal is inputted in a Goertzel filter (S5), and an envelope of the output is detected with a peak detector (S6), and then a differential value of the envelope is acquired using a differentiator (S7). As a result, a first determination part determines that a tone signal component has been detected if the differential value keeps a predetermined threshold value or higher (S12-S13-S15). Thus, detection of a tone signal is confirmed only by addition process without performing multiplication, resulting in lower calculation cost and higher speed. <P>COPYRIGHT: (C)2012,JPO&INPIT |
